This invention relates to improved video-type computer systems and the like, and more particularly relates to a simplified circuit for recovering stored video data signals.
It is well known that video-type displays are preferred for computer games and so-called "home" computers, and that there is an increasing demand in this market for systems which exhibit more complex video images. It is a relatively simple task to produce a video image having increased resolution, provided that cost is not a factor. However, the home computer market is characterized by stiff price resistance above a certain level, and therefore there is a need for new and simpler designs to achieve this objective.
The problem is basically concerned with the storage circuit which holds the video signals or data sought to be presented on the CRT screen. It is well known that the complexity of the video image is a function of the number of pixels on the CRT screen, and it is further well known that the associated storage circuit must employ at least as many memory cells as there are pixels on the CRT screen. Accordingly, if the number of pixels is sought to be increased for this purpose, then a corresponding increase must be made in the number of memory cells in the storage circuit. Unfortunately, this results in an increase in the cost of the storage circuit which is disproportionate to the improvement in the resolution of the image, not only because of the need for more memory cells in the system, but also because of a need for more complex circuits for recovering data signals stored in the memory circuit.
The problems, which attend an increase in the number of memory cells, also relate to an increase in defective assemblies. This is because most storage circuits employ "RAM chips" of conventional design, and these components are conventionally fabricated with pin-type input and output terminals. A pin-type terminal is difficult to fabricate without defects, and if the chip is required to have an increased number of these terminals, it is clear that an increase in the number of pin-type terminals will necessarily increase the chances of a defect in the individual memory chips. Accordingly, it will further be apparent that if it is necessary to increase the number of memory cells in the storage circuit, this will increase the manufacturing cost of the overall system.
These disadvantages in the prior art are overcome or mitigated with the present invention, however, and simpler and more reliable storage circuitry and technique are herewith provided.
A video display system employing a bit-mapped dual-ported video memory having both serial and parallel access is disclosed in U.S. patent application Ser. No. 427,236, filed Sept. 29, 1982 (now U.S. Pat. No. 4,562,435) by McDonough, Laffitte and Hughes, assigned to Texas Instruments.